This application is entitled to the benefit of the filing date of, and hereby incorporates by reference the subject matter disclosed in, Japanese Patent Application No. 11-282359 filed on Oct. 4, 1999, as well as International Application No. PCT/JP00/06897 filed on Oct. 4, 2000.
The present invention relates to a positioning method and an apparatus to measure a position of a signal source moving on the earth""s surface, on the surface of water, or in the air.
In recent years, a position tracking system to track the movement of wild animals in order to protect the same, and for ecological research thereof, has been developed. For instance, to research the ecology and behavior of whales, a transmitter is attached to a whale, so that a radio wave output from the transmitter is received by a receiver provided in an aircraft or a vessel to obtain positional data of the transmitter to thereby track the position of the whale. In this tracking system, it is impossible to simultaneously track a number of individual whales ranging over a large area. Furthermore, the tracking system using an aircraft or vessel is suitable for tracking for a short period of time, but it is difficult to continuously carry out the tracking for a long time, e.g., several months. Moreover, it is extremely difficult to track birds having a high moving speed and wide home range even for a short period of time. In addition, data obtained by the tracking must be transferred from the aircraft or vessel to researchers in a ground facility by a transmission device, which proved to be very inconvenient.
A portable GPS (Global Positioning System) receiver which is designed to receive a GPS signal from a GPS (NAVSTAR) satellite in order to obtain positional data has been developed. However, it is necessary for the GPS receiver to receive GPS signals from at least four satellites in order to measure a position on earth. To this end, the GPS receiver must receive the GPS signals for a long time. Therefore, it is difficult to track an animal such as a whale that appears on the sea surface for a very short period.
Moreover, it is difficult to miniaturize an antenna of the GPS receiver which receives weak GPS signals, and accordingly, it is difficult to make a small GPS receiver. This makes it impossible to attach the GPS receivers to small animals such as birds.
It is an object of the present invention to eliminate the drawbacks mentioned above by providing a positioning satellite system in which the position of an animal can be continuously tracked for a long time, regardless of the speed or range of the movement of the animal, and in which the signal source to be attached to the animal can be made small.
To achieve the object mentioned above, according to an aspect of the present invention, a satellite system is provided, including a signal source located on or in at least one of a surface of the earth, a surface of water, and the air, the signal source including a transmitter device for emitting a radio wave signal having a predetermined frequency and an identification code corresponding to a specific objective; an orbiting satellite for measuring a position of the signal source, the orbiting satellite including a GPS receiver which receives GPS signals from a GPS satellite system to measure the position of the orbiting satellite, a frequency measuring device for receiving the radio wave signal emitted from the signal source to measure the frequency of the radio wave signal, a memory for storing frequency data measured and obtained by the frequency measuring device and position data measured and obtained by the GPS receiver upon measurement of the frequency of the radio signal, and a transmitting device for transmitting the data stored in the memory toward the earth""s surface; and a ground station having a signal receiving device for receiving the data transmitted from the orbiting satellite, the ground station including a computer for calculating the position of the signal source based on the received data of the signal device.
Preferably, the frequency measuring device includes a phase-lock loop receiver.
Preferably, the frequency measuring device and the GPS receiver carry out several measurements of the radio wave signals emitted from the same signal source during the movement of the orbiting satellite, on and along the same orbit, on which the frequency measuring device and the GPS receiver are provided so that the measurement data of each measurement is stored in the memory.
Preferably, the orbit of the orbiting satellite is a polar orbit or sub-recurrent orbit.
The computer can measure the position of the signal source based on reference frequency data of the radio wave signal emitted from the signal source; wherein the frequency data is measured by the frequency measuring device, and the position data of the orbiting satellite is measured by the GPS receiver.
Preferably, the orbiting satellite includes a signal receiving device for receiving the radio wave signal emitted from the ground station; the ground station including a transmitting device for transmitting a specific command to send the data stored in the memory of the orbiting satellite; and the orbiting satellite transmitting the data stored in the memory via the transmitting device upon receipt of the specific command through the signal receiving device.
Preferably, when the radio wave signal of the predetermined frequency is emitted, the signal source sends an identification signal to identify the signal source by the radio wave signal.
According to another aspect of the present invention, a satellite system is provided, including a signal source located on or in at least one of a surface of the earth, a water surface, and the air; and an orbiting satellite for measuring a position of the signal source, the orbiting satellite including a GPS receiver which receives GPS signals from a GPS satellite system, a frequency measuring device for receiving a radio wave signal emitted from a ground signal source on the earth to measure the frequency of the radio wave signal, a memory for storing frequency data measured and obtained by the frequency measuring device and position data measured and obtained by the GPS receiver upon measurement of the frequency, and a transmitting device for transmitting the data stored in the memory toward the earth""s surface.
According to another aspect of the present invention, a ground station is provided, including a signal receiving device for receiving data transmitted from an orbiting satellite; and a computer for analyzing the data received by the receiving device. The orbiting satellite includes a GPS receiver which received the GPS signals from a GPS satellite system to measure the position of the orbiting satellite; a frequency measuring device for receiving the radio wave signal emitted from signal source located on or in at least one of a surface of the earth, a surface of water, and the air, to measure the frequency of the radio wave signal; a memory for storing frequency data measured and obtained by the frequency measuring device and position data measured and obtained by the GPS receiver upon measurement of the frequency of the radio signal; and a transmitting device for transmitting the data stored in the memory toward the earth""s surface.